Image generation apparatus, image generation system and image synthesis method

ABSTRACT

A surveillance system includes an image deformation unit for deforming the image captured or picked up by a surveillance camera so that the appearance of a specified region within this image has the same geometric shape as that of its corresponding region on the map, and an image synthesis display unit operable to extract the specific region of the deformed image and synthesize it in the corresponding map region for on-screen visualization, obtaining the mutual relationship of a plurality of images.

INCORPORATION BY REFERENCE

The present application claims priority from Japanese applicationJP2004-097560 filed on Mar. 30, 2004, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

This invention relates to an apparatus, system and method for combiningtogether images taken by camera devices placed at a plurality oflocations to generate for display a synthesized or composite image. Moreparticularly, the invention relates to a surveillance camera system anda surveillance camera image display method.

A surveillance work by means of a surveillance system using monitorcameras generally includes performing image acquisition by use of atleast one or more surveillance cameras capable of capturing a portion orthe entirety of an area under surveillance, and also includes displayingthe captured scene images on a video image display device such as acathode ray tube (CRT) that is installed at a remote location where asecurity officer or “surveillant” is present by simultaneouslydisplaying multiple monitor camera-captured images at divided screenportions or alternatively by sequentially displaying the monitor cameraimages so that a selected one of them is displayed at a time whileswitching it to another, to thereby recognize and judge the occurrenceof a critical event such as an unusual situation happened within thesurveillance area. In such the surveillance work through observation ofthe monitor camera images, the human being who is a surveillant usesthree kinds of information items—i.e., i) the imaging condition as tothe surveillance area of interest that is being captured or“photographed” from which camera position at what view angle for whichrange of the area, ii) the captured image information per se, and iii)known information concerning the monitor camera'installation location—tomake a comprehensive judgment for understanding and recognizing theevent that presently happens in the surveillance area.

To do this, known surveillance systems are typically designed to employa method for displaying on a video display device the three kinds ofinformation—namely, the surveillance camera's imaging conditions,captured images, and known information as to the surveillancelocations—while dividing the display screen into portions for respectivevisualization or a method for representing the information on asurveillance area as a map and for diagrammatically showing on the mapthe imaging conditions by use of symbols while letting the video imageof a selected camera be displayed in a separate window (for example, seeJP-A-6-284330, JP-A-2003-134503, JP-A-2002-77889, and JP-A-2002-344929).

In addition, there is known a technique for use in a surveillance systemfor airports, rivers, harbors or the like with relatively lessobstructions within a range under surveillance. This technique uses aplurality of cameras with different picture angles to provide multiplecaptured scene images of a wide surveillance area, for reconstructingsuch images into a single image being viewed from a certain point andthen synthesizing the entire surveillance area into a map being lookedat from its overhead direction (see JP-A-2001-319218).

With the above-noted related arts, each is designed to display acamera-captured scene image in its native or “raw” form. For thisreason, even when indicating with the aid of symbols the imagingconditions such as the imaging direction of a surveillance camera on amap indicative of the surveillance range, the surveillant is stillrequired to carry out a series of recognition processes because of thelack of the matching or consistency in geometric relationship betweenthe captured images and the map, which processes may include attemptingto imagine or “re-image” the map-indicated surveillance range into avisual appearance of the monitor range in the case of looking at fromthe same view point as the monitor camera, comparing such the image tothe actually captured surveillance image, and then recognizing an eventthat presently occurs within the surveillance range. Thus thesurveillant is compelled to keep high concentration power constantly.This would cause problems, such as a risk that he or she is likely tocommit judgment mistakes.

In addition, in cases where an increased number of obstructions such aspublic buildings or else are present in the surveillance range, theinconsistency or mismatch in geometric relationship between thesurveillance camera-captured image and the map information can sometimestake place in a way depending upon the conversion processing to beperformed during visual reconstruction into a single image.

Additionally, in the case of such mismatch of the geometric relationshipbetween images captured by a plurality of cameras from differentpositions, the above-identified Japanese patent documents fail toprovide any feasible solutions thereto.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method forsynthesizing and displaying within a map the acquired images of aplurality of surveillance cameras in an easy-to-see way. Another objectof the invention is to provide a surveillance system that enablesimplementation of the display method.

To attain at least one of the foregoing objects, a surveillance systemof this invention is arranged to include more than one surveillancescene imaging unit, a transfer unit for sending forth an image acquiredby the imager unit toward a surveillance center, an imagereceive/storage unit for receiving the image sent by the transfer unitand for storing therein the received image, an image deformation unitfor deforming the image so that the visual appearance of a specificregion within the image is the same in geometric shape as itscorresponding region of a map, a partial image extraction unit forextracting a specific region of the deformed image in accordance withmask information that designates the specific region, and an imagesynthesis and display unit for synthesizing the partial extracted imageof the deformed image into its corresponding region of the map and fordisplaying it.

The system is such that respective scene images, which are acquired orcaptured by several imaging units being different from each other inimaging direction and imaging position plus imaging view angle, are eachdeformed by the image deformation unit in such a way that the visualappearance of a specific region within the image of interest is matchedwith the same geometric shape as its corresponding region within the mapwhereas the partial image extraction unit extracts a specific region ofthe deformed image while the image synthesis/display unit synthesizesfor display this extracted partial image into its corresponding regionwithin the map. Thus, it is no longer required for operators to performthe reading and understanding of images while taking into considerationthe individual imaging unit's image acquisition conditions.Simultaneously, it is also possible to readily recognize and grasp themutual relationship of imaging ranges of respective images within themap.

According to this invention, it becomes possible to readily obtain themutual relationship of a plurality of images on the map.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a surveillance system inaccordance with an embodiment of this invention.

FIG. 2 is a data flow diagram of a surveillance camera image displayingmethod also embodying the invention.

FIG. 3 is a diagram showing an exemplary on-screen image of a bird's eyeview of a city block with buildings while indicating therein camerainstallation locations.

FIG. 4 shows a map image of the same city block with the cameralocations added thereto.

FIG. 5 is an example of a surveillance area image taken from asurveillance camera at an installation location 303.

FIG. 6 shows an on-screen image with geometric conversion appliedthereto for causing the shape of a road portion of a scene imagecaptured by the surveillance camera at the location 303 to be matchedwith the shape of its corresponding road part of the map and also showsthe converted image's layout on the map.

FIG. 7 is an exemplary surveillance area image as taken from asurveillance camera at an installation location 304.

FIG. 8 is an image with geometric conversion applied thereto for causingthe shape of a road of an image picked up by the surveillance camera atthe location 304 to be identical to the shape of its corresponding roadpart of the map and also shows its layout on the map.

FIG. 9 is a pattern of mask information on the map indicating theimaging range of a road portion that is capturable by the surveillancecamera at the location 303.

FIG. 10 is a pattern of mask information on the map indicating theimaging range of a road portion that is takable by the surveillancecamera at the location 304.

FIG. 11 is an on-the-map synthesized display of an image resulted fromcropping only road part from an image that causes the geometric shapesof road portions captured by the surveillance cameras at the locations303 and 304 to match with the map, respectively.

FIG. 12 shows coordinate systems that are set up to the on-the-map roadpart image and the map respectively in order to define the conversionfor matching the road part shapes of the surveillance camera images withthe road part image on the map along with an intermediate coordinatesystem used to calculate an equation for such conversion.

FIG. 13 is a surveillance image display screen of the surveillancesystem of the invention.

FIG. 14 is a functional block diagram of a network surveillance camerafor use in a second embodiment of the invention.

FIG. 15 is a flow chart for explanation of an operation of the networksurveillance camera of the invention in a synchronous reference mode.

FIG. 16 is a flowchart for explanation of an operation of the networksurveillance camera of the invention in a sync slave mode.

FIG. 17 is an explanation diagram of the communication timing andcommunication contents between the camera operable in the synchreference mode and the camera operable in the sync slave mode.

FIG. 18 is a graph showing a change with time of an output value of amultiplication and division unit 1426.

FIG. 19 is an explanation diagram of an internal configuration of avideo collecting/browsing server 120.

FIG. 20 is an explanation diagram of a storage form of projectionconversion parameters in units of surveillance cameras.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Currently preferred embodiments of the invention will be explained withreference to the accompanying drawings below.

Embodiment 1

Referring to FIG. 1, there is shown a configuration of a surveillancesystem which collects surveillance camera images via a network,synthesizes them into map data, and visually displays an image thussynthesized. A plurality of network video cameras 101, 102, 103 transmittheir acquired images to a video image collecting and browsing server120 over a network 104. The network camera 101 acquires a scene image byusing a camera 110, performs compression encoding of the image data byan image encoder 111, and sends forth the captured or “photographed”image data to the network through a network adapter 112. The videocollecting/browsing server 120 is equipped with an external storagedevice 124 for storing therein several information items such asaccumulative surveillance camera image data 132, map data 131 of an areaunder surveillance, per-camera conversion parameters 130 necessary forthe synthesis of a camera-captured image and map data, per-camera maskinformation 133 for designating the range of a camera-shot image forsynthesis to the map data, and an image processing software program 134of the invention. The server 120 also includes a display unit 121 forvisually displaying map information and/or surveillance area images,along with a keyboard 123 and a mouse device 122 for entry ofinstructions as to a display method and others. Note here that the databeing stored in the external storage device 124 may alternatively beheld in an internal memory that is built in the videocollecting/browsing server 120. In this system, processing is done tocollect captured image data, synthesize such collected multiple imagesinto map data, create a new image through the synthesis, and thendisplay it.

An internal structure of the video collecting/browsing server 120 willbe explained by use of FIG. 19. This video collect/browse server 120includes a central processing unit (CPU) 1901, a memory 1902, a networkinterface circuit 1903 connectable to the network for transmitting andreceiving data, a disk interface circuit 1904 for sending and receivingdata to and from the external storage disk device 124, a keyboardinterface circuit 1905 for connecting the keyboard 123, a mouseinterface circuit 1906 for connecting the mouse 122, and a videointerface circuit 1907 that enables connection of the image displaydevice 121 for displaying an image or images on its screen. These partsor components are interconnected together via a bus 1910.

Next, an explanation will be given of a flow of the image processingprocedure of the video collecting/browsing server 120 with respect tosurveillance camera-acquired images in this surveillance system, withreference to a data flow diagram of the surveillance image processingshown in FIG. 2. Assume that the data sent via the network to the videocollect/browse server 120 are camera 1 imaging data 201, camera 2imaging data 202, and camera N imaging data 203. These camera imagingdata are accumulatively stored in the external storage device 124 byreceive/storage processing 211 as stored image data 204 or,alternatively, are utilized on a real time basis as input data ofprojection conversion processing 212 for the synthesis with a map andfor display of a synthesized image. The projection conversion processing212, whose inputs are stored image data 204 and the parameters 206 ofthe projection conversion, performs geometric deformation processing forprojection conversion of a surveillance camera image to bemap-synthesized and displayed on the display device 121, based on aconversion parameter 206 corresponding to the surveillance camera ofinterest. Regarding the output image data of the projection conversionprocessing 212, the surveillance camera image is processed by synthesisprocessing 213 to be buried for synthesis into a map image, while usingmap data 205 of an area of the surveillance image acquisition and maskinformation 207 necessary for synthesizing the geometrically deformedsurveillance camera image onto the map data. A composite image resultedfrom the synthesis of the map and the camera image is displayed on thedisplay device 121 by display processing 214. The image processingprogram 134 of the invention which describes the image processing shownin FIG. 2 is stored in the external storage device 124 connected to thevideo collect/browse server 120, and loaded upon execution into thevideo collect/browse server 120 and then executed by a control unitthereof. In short, the video collect/browse server 120 is an apparatusthat generates an image(s).

Subsequently, in relation to surveillance objects to be monitored bysurveillance cameras and surveillance camera installing locations,explanations will be given while using a bird's eye view diagram in FIG.3 and using a map in FIG. 4. In FIG. 3, a scenery of buildings standingin a city block is depicted in the form of a bird's-eye view. Blackcircular marks 301 to 307 in this drawing indicate the installationlocations of the surveillance cameras that are set at the rooftops ofbuildings in order to capture or “shoot” scene images on roads aroundthe buildings. In FIG. 4, a pictorial representation is shown by meansof a map of the city block shown in FIG. 3.

The installation locations of the surveillance cameras shown in FIG. 3are indicated by black circles with the same numbers as those in FIG. 3being added thereto. Exemplary surveillance camera-captured scene imagesof the city block such as shown in FIG. 3 or FIG. 4 are shown in FIG. 5and FIG. 7. In FIG. 5, there is shown a photo image of roads aroundbuildings, which image was captured by a surveillance camera that is setat the camera installation location 303. Shown in FIG. 7 is a photoimage of a street near a building, which was shot by a monitor camerathat is placed at another camera installation location 304. As thesemonitor cameras are different from each other in imaging direction andimaging height and also imaging view angle, it is not easy for asurveillant to find out and understand that each scene image was takenfrom which building facing which road for which range thereof whilevisually comparing these images to the city block information shown inFIGS. 3 and 4. In this way, in order to understand from multiple monitorcamera images the situation of a surveillance area being captured by themonitor camera of interest, the surveillant is required to do a readingcomprehension work that demands concentration power, which task includesthe steps of deeply understanding in advance the map information of suchsurveillance area and differences of each surveillance scene image inimaging location and imaging direction, and then interpreting eachsurveillance image while conceiving in his or her head which one ofrespective surveillance images exactly corresponds to which range on themap. Due to this, in order to fulfil a surveillance business task usingthe monitor cameras, the surveillant who is expected to performsurveillance activities using such monitor cameras is compelled to doworks that require high concentration power to complete the reading andcomprehension of every monitor image. Consequently, when she/he dropsdown in concentration power, this often leads to occurrence of adecrease in quality of surveillance works-for example, the lack of anability to accurately perform the expected image reading andcomprehension, or merely viewing the monitor images without aim.

See FIG. 6, which shows an exemplary on-screen image in which a photoimage 601 that is obtained by applying certain projection conversion tothe surveillance scene image of FIG. 5 is laid out in such a manner thatits road portions coincide with those on the map of FIG. 4. Thegeometrical conversion for letting the road image portions coincide withcorresponding road parts of the map is uniquely determinable fromprojection conversion that is determined depending upon the installationlocation and direction of a surveillance camera with respect to the roadground plane and the characteristics of a lens attached to the monitorcamera and also geometric conversion that was used for map drawing.Generally, in the map of a range that is narrow enough to neglect theinfluence of a spherical shape of the surface of Earth, such as the oneshown in FIG. 4, the geometric conversion used for map preparation isregarded as parallel projection, which becomes a type of projectionconversion. For this reason, the camera monitor image and map'srespective road shapes on the earth surface plane become the shapes thatare converted from the shapes of real roads or streets by differentprojection conversion schemes.

Between two geometrical relationship obtained by converting a givenplanar geometric relationship by two different projection conversionmethods, a projection conversion capable of converting one geometricrelationship into the other geometric relationship is available. Owingto this nature, as shown in FIG. 6, concerning the geometricrelationship on a flat plane such as a road, there must exist aprojection conversion which can convert a camera-captured road imageinto an image enabling it to coincide with a road that is depicted as amap.

Similarly, in FIG. 8, there is shown an on-screen image in which a sceneimage 801 that is obtained by applying a selected kind of projectionconversion to the surveillance image of FIG. 7 is disposed on the map ofFIG. 4 in such a manner that the geometrical relationships of roadportions are matched together. As shown in FIG. 6 or FIG. 8, the sceneimage which was projection-converted to allow the captured image of aroad portion to coincide with a road part on the map is such that onlythe geometrical relationship on the same plane on which the road existsis matched with the map. Accordingly, those image portions that do notexist on the same plane as the road, such as the building's side facesand rooftop or else, fail to coincide with the geometrical relationshipof their corresponding parts as depicted on the map even after theprojection conversion.

In the case of two-dimensional (2D) projection conversion for convertingthe above-noted images, unique determination is usually establishableupon determination of the relationship of four separate points on theplanes of a conversion source and a converted one. Thus, the projectionconversion for converting so that the captured image of a road portioncoincides with a road portion on the map is uniquely determinable by aprocedure having the steps of selecting from the road portion on theground surface plane of a surveillance image any arbitrary four pointshaving the nature that a set of any three points are hardly alignedalong a straight line, and then correlating four points on the map tosuch four points thus selected.

A method for determining such the projection conversion will beexplained using FIG. 12. FIG. 12 shows a scene image 1201 which wasacquired by a surveillance camera in which an image coordinate system Lhaving an x coordinate axis 1211 and a y coordinate axis 1212 isdefined, a map 1202 that is captured by a monitor camera in which animage coordinate system M having its x coordinate axis 1221 and ycoordinate axis 1222 is defined, and a 2D plane 1203 in which an imagecoordinate system K having its u coordinate axis 1231 and v coordinateaxis 1232 is defined.

A conversion formula which represents projection conversion H forletting four points a (1213), b (1214), c (1215), d (1216) within theimage 1201 correspond to four points A (1223), B (1224), C (1225), D(1226) in the map 1202 becomes an extremely complex conversion equation.In view of this, two projection conversion schemes—i.e., projectionconversion G of from the coordinate system L of the image 1201 into thecoordinate system K of 2D plane 1203 such as shown in Expression (1),and projection conversion F from the coordinate system K of image 1203to the coordinate system M of map 1202 shown in Expression (2)—areobtained respectively to thereby obtain a synthesized mapping image Hshown in Expression (3). This synthetic mapping image H becomesprojection conversion. As shown in Expression (4), it becomes projectionconversion H of from the coordinate system L of the image 1201 to thecoordinate system M of map 1202.

Coordinate Coordinate System L System K G: (x, y) → (u, v) (1)Coordinate Coordinate System K System M F: (u, v) → (X, Y) (2) H = FoG(3) Coordinate Coordinate System L System M H: (x, y) → (X, Y) (4)

As shown in Expression (5), the projection conversion F is defined asprojection conversion for causing four points 1233, 1234, 1235 and 1236having “uv” coordinate values (0,0), (0,1), (1,0) and (1,1) respectivelywithin the 2D plane 1203 to correspond to the four points A (1223), B(1224), C (1225), D (1226) within the map 1202. Here, suppose that thefour points A (1223), B (1224), C (1225), D (1226) in the map 1202 haveXY coordinate values (0,0), (X2,Y2), (X3,Y3) and (X4,Y4) in thecoordinate system M, respectively.

Coordinate Coordinate System K F System M (0, 0) → Point A (0, 0) (1, 0)→ Point B (X2, Y2) (1, 1) → Point C (X3, Y3) (5) (0, 1) → Point D (X4,Y4)

Further, as shown in Expression (9), the projection conversion G isdefined as projection conversion for letting four points a (1213), b(1214), c (1215), d (1216) within the image 1201 correspond to fourpoints 1233, 1234, 1235, 1236 having uv coordinate values (0,0), (0,1),(1,0) and (1,1) respectively within the 2D plane 1203. Suppose here thatthe four points a (1213), b (1214), c (1215), d (1216) within the image1201 have xy coordinate values (0,0), (x2,y2), (x3,y3) and (x4,y4) inthe coordinate system L, respectively.

Coordinate Coordinate System L G System K Point a (0, 0) → (0, 0) Pointb (x2, y2) → (1, 0) Point c (x3, y3) → (1, 1) (9) Point d (x4, y4) → (0,1)

A practically implemented equation of the above-defined projectionconversion F for conversion from the coordinate value (u,v) of thecoordinate system K to the coordinate value (X,Y) of the coordinatesystem M is shown in Expression (8). Here, coefficients P1, Q1, P2, Q2,P0, Q0, R0 are defined, as indicated on Expression (7), using auxiliaryconstants T1, T2, T3, T4 that are indicated in Expression (6) as definedby the expression of the coordinate values of the points A (1223), B(1224), C (1225), D (1226).

$\begin{matrix}\left\{ \begin{matrix}{{T\; 4} = {{X\; 2*Y\; 3} - {X\; 3*Y\; 2}}} \\{{T\; 3} = {{X\; 2*Y\; 4} - {X\; 4*Y\; 2}}} \\{{T\; 2} = {{X\; 3*Y\; 4} - {X\; 4*Y\; 3}}} \\{{T\; 1} = {{T\; 4} + {T\; 2} - {T\; 3}}}\end{matrix} \right. & (6) \\\left\{ \begin{matrix}{{{P\; 1} = {T\; 2*X\; 2}}\;} \\{{Q\; 1} = {T\; 4*X\; 4}} \\{{P\; 2} = {T\; 2*Y\; 2}} \\{{Q\; 2} = {T\; 4*Y\; 4}} \\{{P\; 0} = {{T\; 2} - {T\; 1}}} \\{{Q\; 0} = {{T\; 4} - {T\; 1}}} \\{{R\; 0} = {T\; 1}}\end{matrix} \right. & (7) \\\left\{ \begin{matrix}{X = \frac{{P\; 1*u} + {Q\; 1*v}}{{P\; 0*u} + {Q\; 0*v} + {R\; 0}}} \\{Y = \frac{{P\; 2*u} + {Q\; 2*v}}{{P\; 0*u} + {Q\; 0*v} + {R\; 0}}}\end{matrix} \right. & (8)\end{matrix}$

Similarly, a practical expression set of the projection conversion G forconverting the coordinate value (x,y) of the coordinate system L to thecoordinate value (u,v) of coordinate system K is shown in Expression(12). Here, coefficients p1, q1, p2, q2, p0, q0, r0 are defined, asindicated on Expression (11), using auxiliary constants t1, t2, t3, t4,d1, d2 that are shown in Expression (10) as defined by the equation ofthe coordinate values of the points a, b, c, d.

$\begin{matrix}\left\{ \begin{matrix}{{t\; 4} = {{x\; 2*y\; 3} - {x\; 3*y\; 2}}} \\{{t\; 3} = {{x\; 2*y\; 4} - {x\; 4*y\; 2}}} \\{{t\; 2} = {{x\; 3*y\; 4} - {x\; 4*y\; 3}}} \\{{t\; 1} = {{t\; 4} + {t\; 2} - {t\; 3}}} \\{{d\; 1} = {{t\; 4} - {t\; 3}}} \\{{d\; 2} = {{t\; 2} - {t\; 3}}}\end{matrix} \right. & (10) \\\left\{ \begin{matrix}{{p\; 1} = {{- t}\; 4*t\; 1*y\; 4}} \\{{q\; 1} = {t\; 4*t\; 1*x\; 4}} \\{{p\; 2} = {t\; 2*t\; 1*y\; 2}} \\{{q\; 2} = {{- t}\; 2*t\; 1*x\; 2}} \\{{p\; 0} = {{{- d}\; 1*t\; 4*y\; 4} + {d\; 2*t\; 2*y\; 2}}} \\{{q\; 0} = {{d\; 1*t\; 4*x\; 4} - {d\; 2*t\; 2*x\; 2}}} \\{{r\; 0} = {{- t}\; 4*t\; 3*t\; 2}}\end{matrix} \right. & (11) \\\left\{ \begin{matrix}{u = \frac{{p\; 1*x} + {q\; 1*y}}{{p\; 0*x} + {q\; 0*y} + {r\; 0}}} \\{v = \frac{{p\; 2*x} + {q\; 2*y}}{{p\; 0*x} + {q\; 0*y} + {r\; 0}}}\end{matrix} \right. & (12)\end{matrix}$

Then, the projection conversion H that correspondingly converts thecoordinate value (x,y) of the coordinate system L to the coordinatevalue (X,Y) of the coordinate system M for letting four points a (1213),b (1214), c (1215), d (1216) within the image 1201 correspond to fourpoints A (1223), B (1224), C (1225), D (1226) on the map 1202 can becalculated by first using Expression (12) to obtain a coordinate value(u,v) from the coordinate value (x,y), and then using Expression (8) toget a coordinate value (X,Y) from the coordinate value (u,v). Theconversion with two such projection conversions G and F being combinedtogether in this way becomes projection conversion, resulting in theprojection conversion H having a form that is representable by nineconstant coefficients a0, a1, a2, b0, b1, b2, c0, c1, c2 of Expression(13).

$\begin{matrix}\left\{ \begin{matrix}{X = \frac{{a\; 1*x} + {b\; 1*y} + {c\; 1}}{{a\; 0*x} + {b\; 0*y} + {c\; 0}}} \\{Y = \frac{{a\; 2*x} + {b\; 2*y} + {c\; 2}}{{a\; 0*x} + {b\; 0*y} + {c\; 0}}}\end{matrix} \right. & (13)\end{matrix}$

The nine constant coefficients included in Expression (13) becomepractical representation of the per-camera conversion parameters 130 ofFIG. 1. In FIG. 20, conversion parameter tables are shown, each of whichstores in table form the nine constant coefficients included inExpression (13) in units of surveillance cameras. Tables 2001, 2002 and2003 are conversion parameter data forms with respect to the monitorcameras 1, 2 and N, respectively.

Upon determination of the above-defined equation between the coordinatesfor making a road portion of surveillance camera image correspond to aroad indication part on the map, it is readily realize the projectionconversion processing 212 that is shown in FIG. 2 as an image processingprogram for deforming image shapes, typically called the geometricaldeformation processing, which is executable in the videocollecting/browsing server 120 of FIG. 1.

Subsequently, the synthesis processing 213 of FIG. 2 will be explained.This synthesis processing is aimed at using a surveillance camera imagethat was geometrically deformed by the projection conversion processing212 to thereby synthesize onto the map of FIG. 4 only road portions of apartial image that is identical in geometric shape to the map. For thispurpose, firstly as shown in FIG. 9 and FIG. 10, prepare an image mask,such as 901 or 1001, for each of all the surveillance cameras involved,which mask indicates certain region equivalent to a road portion beingacquired by the surveillance camera 303 or 304. Then, let it be the maskinformation 207 of FIG. 2. If the monitor cameras are fixed ininstallation position and imaging direction plus imaging picture angle,then the image masks 901 and 1001 are constant. Accordingly, as far asthe imaging direction and imaging picture angle are forced to stayconstant, the mask information may be once set up and prepared uponinstallation of such monitor cameras.

The projection-converted images 601 and 801 shown in FIGS. 6 and 8 areprocessed to extract only the images of certain portions that aredesignated by the image masks 901 and 1001 shown in FIGS. 9 and 10,respectively. Then, combine them onto the map of FIG. 4. The resultanton-screen display thereof becomes an image portion 1101 shown in FIG.11.

Next, the display processing 214 of FIG. 2 will be explained by use ofFIG. 13. FIG. 13 is an exemplary on-screen display image of the displaydevice 121 of FIG. 1. On its screen 1300, there are laid out i) a mapand monitor image synthesis display window 1310 in which the above-notedimage with each surveillance camera image being geometrically deformedthrough appropriate projection conversion on the surveillance city blockmap while excluding any portions that are absent on the same plane asthe road ground surface is synthetically displayed at the road portionson the map while having correct geometrical compliance or consistency,ii) a surveillance camera image non-conversion display window 1320 fordirectly displaying a native version of each monitor camera image, iii)a present time display window 1307 for displaying a present time, andiv) an imaging time display window 1308 for displaying the imaging timepoint of a presently displayed monitor camera image.

The imaging time display window 1308 contains therein an imaging timechange up/down button 1309 used to set a designated imaging time pointfor extraction from a specific time-captured image of the accumulatedimages 132 that have been stored in the external storage device 124 ofFIG. 1 as the monitor camera images within the map/monitor synthesisdisplay window 1310 and monitor camera image non-conversion displaywindow 1320 other than a real-time image at the present time point beingdisplayed.

Within the monitor camera image nonconversion display window 1320, thoseimages of surveillance cameras with unique monitor camera numbers addedthereto, which images are acquired at the time point being presentlydisplayed in the imaging time display window 1308, are laid out inindividual camera captured image display windows 1301, 1302, 1303, 1304,1305 in such a manner that these are aligned and queued in an ascendingorder of the camera numbers in a top-to-bottom ranking fashion. Forthose monitor camera-captured images that cannot be displayed within thewindow 1320, a scroll bar 1306 is manually operated to increase ordecrease the monitor camera number to be displayed in the uppermostcamera captured image display window 1301 whereby the camera numbers ofthe other camera captured image display windows 1301-1305 are alsomodified to thereby display within the window 1320 a monitorcamera-captured image having a desired camera number.

In this way, it is possible to synthesize or merge onto the map theimage obtained by removal of certain portions that are absent in thesame plane as the road ground surface from an image to which theprojection conversion 212 suitable for a respective one of the monitorcamera images was applied. Thus the mutual relationship of respectivemonitor camera images is consistently matched on the map in a unifiedmanner so that it becomes possible to visually monitor on the map a roadsituation within the surveillance area.

According to this embodiment, the surveillant is no longer required toread and understand surveillance camera images in accordance with thecharacteristics unique to such monitor cameras, such as the location andimaging direction of each camera of the system.

Embodiment 2

In the surveillance system explained in Embodiment 1, in cases where ascene image acquired by the surveillance camera 303 that is installed inthe city block shown in FIG. 3 and an image captured by the monitorcamera 304 are different in imaging time from each other, it is hardlyexpected to display the status at a given instant in the entirety of thesurveillance area. For this reason, in the image with road status imagesof two separate cameras being synthesized together as shown in FIG. 11,the image portion of a moving object, such as for example a landvehicle, is photographed so that the same automobile was present atdifferent road surface positions in the overlapped part of the maskinformation 901 and mask information 1001. This causes in some cases aproblem in quality of the image synthesized, such as undesired synthesisand display thereof in a double offset manner like a ghost.

Consequently in the second embodiment, its feature lies in that themonitor cameras 101, 102, 103 in the surveillance system shown in FIG. 1are made up of a certain type of cameras capable of establishing mutualsynchronization of the frame timing during motion picture or videoacquisition. For the other matters, the surveillance system is similarto Embodiment 1 in system arrangement and also in surveillance imagedisplay method for use therein. An example of the implementation of aplurality of surveillance cameras with such mutual synchronizability invideo imaging operations will be explained with reference to some of theaccompanying drawings below.

FIG. 14 shows, in function block diagram form, a configuration of anetwork-linked surveillance camera indicating an embodiment of thisinvention. This network monitor camera embodying the invention isgenerally made up of a built-in computer block 1400, an image datageneration block 1410, and a phase-controllable synchronization signalgeneration block 1420.

The built-in computer block 1400 includes a central processing unit(CPU) 1402, random access memory (RAM) 1403, disk control interface 1404and network interface 1406, which are connected together via an internalbus 1401. As in currently available general-purpose computers, thecomputer block 1400 functions to load any given program code, which isstored in a hard disk 1405 that is connected through the disk controlinterface 1404, into the RAM 1403 for enabling the CPU to execute theprogram code. Furthermore, let the hard disk 1405 store therein anoperating system (for example, Linux™ or else) which includes a softwareprogram module necessary for communicating with an external networklinkable via a network link terminal 1407 and a program module capableof exchanging data between itself and any one of the image datageneration block 1410 that is connected via the internal bus 1401 andthe phase-controllable synchronization signal generation block 1420.Upon startup, the operating system (OS) is loaded and then renderedoperative, causing a video image acquisition synchronizing program tooperate under the control of the OS in a way as will be discussed below.

The image data generation block 1410 is configured from a camera module1411 capable of controlling the imaging timing by supplying a respectiveone of vertical and horizontal synchronization signals, an image encoder1412 for conversion to various kinds of industry standard image dataformats with or without compression capability (e.g., JPEG), and a framenumber generator 1413 operable to calculate a frame number based oncounter information of the synch signal generation block 1420. A digitalvideo signal as output from the camera module 1411 and frame numberinformation as output from the frame number generator 1413 are takeninto the image encoder 1412 for conversion to digital data with a properimage data format, which data is passed via the internal bus 1401 andthen read into the built-in computer block 1400 for transmission to theexternal network by way of the network interface 1406.

The phase-controllable sync signal generation block 1420 includes animage reference clock generator 1421, a 32-bit accumulative counter 1422which adds 1, once at a time, to a pulse signal generated by the blockgenerator, an offset register 1424 capable of setting a 32-bit integervalue from the built-in computer block 1400, an adder 1423 for addingtogether a count value of the addition counter 1422 and a setup value ofthe offset register 1424, a frequency division ratio 32-bit constantregister 1425 for setting a ratio of a clock cycle or period of theimage reference clock generator 1421 versus the period of a horizontalsync signal being supplied to the camera module 1411, a multiplicationand division circuit 1426 for subtracting an output numeric value of theadder 1423 by a numeric value being presently set at the frequencydivision ratio constant register 1425 and for outputting a calculationresult in the form of a 32-bit data signal, a register 1427 forretaining therein an output value of the multiplier/divider 1426 withina time period equivalent to one cycle of the reference clock, acomparator 1428 which receives at its input node “A” the output value ofthe multiplier/divider 1426 and also inputs an output value of theregister 1427 at its node “B” for outputting a 1-bit data signal oflogic “1” when A is less than B and for outputting a “0” in the otherevents, a monostable multivibrator 1429 for generating a horizontal syncsignal pulse waveform from an output pulse of the comparator 1428, afrequency division ratio 32-bit constant register 1430 for setup of aratio between the periods of a clock signal of the image reference clockgenerator 1421 and a vertical sync signal being supplied to the cameramodule 1411, a multiplier/divider 1431 for subtracting an output numericvalue of the adder 1423 by a numeric value being set at the frequencydivision ratio constant register 1430 and for outputting its calculationresult in the 32-bit data form, a register 1432 for holding an outputvalue of the multiplier/divider 1431 within a time period equivalent toone cycle of the reference clock, a comparator 1433 which receives atits input node A an output value of the multiplier/divider 1431 and alsoinputs an output value of the register 1432 at its node B for outputtinga 1-bit signal of logic “1” when A is less than B and for outputting a“0” in the other cases, and a monostable multivibrator 1434 forgenerating a horizontal sync signal pulse waveform from an output pulseof the comparator 1433.

In the second embodiment, a use form of the network surveillance camerawith image acquisition synchronization functionality is as follows. Itis used by replacing each of the network surveillance cameras 101, 102,103 in the surveillance system configuration diagram of FIG. 1 of thefirst embodiment with the imaging-synchronization function-added networksurveillance camera having its internal configuration shown in FIG. 14.

An operation of the imaging synchronization function-added networksurveillance camera has two types of operation modes as set therein. Oneis a synchronization dependence or “slave” mode; the other is asynchronization reference mode. In the system configuration of FIG. 1,only one of all the network cameras linked to the network 104—forexample, a surveillance camera 101—is designed to operate in the syncreference mode while letting any one of the remaining surveillancecameras 102, 103 operate in the sync slave mode.

The operation of the network surveillance camera of the invention willbe explained using flow charts of FIGS. 15 and 16 in relation to itssync reference mode and sync slave mode, respectively.

In the sync reference mode, let the built-in computer block 1400 executean appropriate program in accordance with the flow chart of FIG. 15.Firstly, at a procedure step 1500, perform the zero-clearing orresetting of the addition counter 1422 and the offset register 1424 ofthe phase-controllable sync signal generation block 1420. Fromimmediately after this step, the addition counter 1422 is operable toincrease its counter value by one at a time with the interval of pulsesto be generated by the image reference clock generator 1421.

At step 1501, read the content of data received from the network, towhich the built-in computer block 1400 is linked. Then at step 1502,determine whether the reception content thus read is a send request froma network camera that is operating in the sync slave mode. If not thesend request, then return to the step 1501. If the received content isthe send request then go to step 1503, which reads an output value ofthe adder 1423 of the phase-controllable synch signal generation block1420. In the sync reference mode the value of the offset register 1424is kept unrevised after the reset and thus stays at zero so that theoutput value of the adder 1423 is identical to the count value ofaddition counter 1422. Then at step 1504, rapidly transmit the readcounter value of addition counter 1422 toward the sync slavemode-operating network camera that has issued the send request.Subsequently, return again to step 1501, for sequentially continuing tosend back the count value of addition counter 1422 in replay to a sendrequest(s).

In the sync slave mode, let the built-in computer block 1400 execute aprogram in accordance with the flowchart of FIG. 16. First, at step1600, clear to zero the addition counter 1422 and the offset register1424 of the phase-controllable sync signal generation block 1420. Fromimmediately after this step, the addition counter 1422 operates toincrease its counter value by one at a time at intervals of pulsesgenerated by the image reference clock generator 1421. At step 1601,substitute zero to a parameter “i” for control of the repeat number of aloop covering from step 1603 up to step 1609. At a conditional branch ofstep 1602, if the parameter i is less than 100 then pass the control toexecution of task part of the following steps 1603 to 1609; if theparameter i is greater than or equal to 100 then jump to step 1610. Atthe first step 1603 of the repeat loop calculation block consisting of aseries of steps 1603 to 1609, the output value of adder 1423 is assumedto be read data “Ai.”

At step 1604, send via the network a request packet for requesting acamera that is operating in the sync reference mode to transmit anoutput value of the adder 1423 of the camera. At step 1605, wait forreception of the information that was requested at step 1604. If suchreception is available then proceed to the next step 1606. At step 1606,let the output value of adder 1423 of the sync reference mode camerawhich is the received information be “Bi.” Then at step 1607, let anoutput value of the adder 1423 of the self camera be read data “Ci.” Atstep 1608, calculate (Bi−(Ai+Ci)/2) to obtain a result, which is givenas Di. At step 1609, increase by 1 the value of i of the repeat numbercontrol parameter; then, return to step 1602. After repeated executionof the series of steps 1603 to 1609 for hundred times, the systemprocedure proceeds to step 1610. At step 1610, use a hundred of databits Di that have been calculated at step 1608 to thereby obtain anaverage value thereof—here, let it be D. At step 1611, set a valueresulted from the addition of the numeric value D to a presently setvalue of the offset register 1424. Whereby, it is expected that theoutput value of adder 1423 is modified so that this value is identical,exactly at this time, to the output value of the adder 1423 of the syncreference mode camera.

At step 1612, wait for the elapse of a predetermined length of time inorder to execute again the above-noted modification procedure with ablank of the predetermined time. Thereafter, return the control to thestep 1601. The fixed length of the wait time is determinable from aclock chop interval difference among the cameras occurring due to anindividual difference of the image sync reference clock 1421 and/or awobble amount of the clock chop interval of each image sync referenceclock 1421. Further, in order to suppress any unwanted increase innetwork traffic, it is recommendable to restrain from performingcommunications for the synchronization purpose at excessively increasedfrequent intervals. By taking account of these conditions, the wait timeof step 1612 is set to range from several tens of seconds to severaltens of minutes.

Using FIG. 17, an explanation will now be given of the principle of anevent that the operation of sync slave mode camera as has been explainedin the flowchart of FIG. 16 results in the output value of adder 1423 ofthe self camera being synchronized with the output value of adder 1423of a sync reference mode camera. In FIG. 17, there are shownside-by-side along a coordinate axis 1701 indicative of time points anaxis 1702 which indicates a change in output value of the adder 1423 ofthe camera operating in the sync slave mode and an axis 1703 indicatinga change in output value of the adder 1423 of the camera operating inthe sync reference mode. Suppose that at a time point t1 on the timeaxis 1701, a request is issued for sending the output value of adder1423 of the sync reference mode camera from the sync slave mode camerato sync reference mode camera at the step 1604 of the flowchart of FIG.16. The output value of adder 1423 of the sync slave mode camera at thistime point t1 is given by “A.” When this send request arrives at thesync reference mode camera at a time point t2, this sync reference modecamera promptly sends back the output value “B” of the adder 1423 towardthe sync reference mode camera. This reply reaches the sync slave modecamera at a time point t3. Assume that an output value of the adder 1423of the sync slave mode camera at such the instant is “C.” At this time,it is assumable that a time (t2−t1) taken for send request communication1704 of from the sync slave mode camera to the sync reference modecamera is equal in length to a time (t3−t2) taken for the reply 1705from the sync reference mode camera to sync slave mode camera. Thus, theoutput value of adder 1423 of the sync slave mode camera at the timepoint t2 is presumed as (A+C)/2. Accordingly, the value (B−(A+C)/2) isconsidered to be a difference at this time point between the outputvalue of adder 1423 of the sync slave mode camera and the output valueof adder 1423 of the sync reference mode camera. It must be noted herethat such the presumption as to the equity of (t2−t1) and (t3−t2) is notalways established because of the presence of influence of communicationenvironments. In view of this fact, another presumption is furtherintroduced, saying that the difference between the values (t2−t1) and(t3−t2) occurring due to the influence of communication environmentstakes place due to probabilistic factors. Based on such presumption, thedifference between the output values of adders 1423 of two separatecameras at the same time point is calculated again and again for hundredtimes to thereby obtain the average value thereof, which is then used asa good estimate value of the difference between the output values of theadders 1423. By adding such the difference between the output values ofadders 1423 thus estimated in this way to a presently set value of theoffset register 1424 of the sync slave mode camera, the output value ofadder 1423 is expected to increase by (B−(A+C)/2), resulting incoincidence with the output value of the adder 1423 of the syncreference mode camera at the same time point. As apparent from theforegoing, the output value of an adder 1423 of every network-linkedcamera operable in the sync slave mode is identical during operation tothe output value of the adder 1423 of the only camera operable in thesync reference mode.

The image reference clock 1421 of every camera is set equal in frequencyto the others. The output value of the adder 1423 of every camera issuch that its value increases one by one at the same time intervals.Letting the time interval for a change of this output value be TC, theinteger ratio of a sync pulse pitch of the horizontal sync signal beinginput to the camera module 1411 with respect to the time TC isrepresented by “M.” This value M is preset to the frequency divisionratio constant register 1425. Doing so may cause an output value of themultiplier/divider 1426 to repeat increment and decrement at timeintervals TH as shown in FIG. 18. With the use of this characteristicfeature, the timing of a decrement of the multiplication/division valueis detectable by allowing the comparator 1428 to compare an output valueof the register 1427 that holds the output value of themultiplier/divider 1426 prior to the reference clock's one cycle time TCto the output value of multiplier/divider 1426, thereby obtaining pulsesof the period TH. The pulses with this period TH are reshaped by usingthe monostable multivibrator into the waveform of horizontal syncsignal, which is then supplied as the horizontal sync signal of thecamera module 1411.

Similarly, an integer ratio of a sync pulse pitch TV of the verticalsync signal being input to the camera module 1411 versus the one cycletime TC of the image reference clock 1421 is given as “N.” This value Nis preset to the frequency division ratio constant register 1430. Inthis case, as in the case of the horizontal sync signal generationstated supra, pulses of the period TV are obtainable as an output of thecomparator 1433. The pulses with this period TV are reshaped by themonostable multivibrator 1434 into the waveform of vertical sync signal,which is then supplied as the horizontal sync signal of the cameramodule 1411.

As previously stated, the output value of the adder 1423 of everynetwork-linked camera operable in the sync slave mode is identicalduring operation to the output value of the adder 1423 of the onlycamera operable in the sync reference mode, whereby the horizontal syncsignal and vertical sync signal which are generated at every camera inthe above-stated way become sync signals that are exactly in phase witheach other. Accordingly, the acquisition timing of an image to becaptured by the camera module 1411 becomes synchronized among thecameras involved. Further, as the frame number generator 1413 isarranged to calculate a frame number based on the output value of theadder 1423 having the same value among the cameras, the frame number isalso capable of generating the same value while offeringsynchronizability among the cameras. A frame number calculation methodis arranged to calculate as the frame number FN a maximal integer valuethat does not exceed a value of (A/f/TV), where “A” is the output valueof adder 1423, f is the clock frequency of the sync reference clock1421, and TV is the period of the vertical sync signal. As for the videodata synchronously acquired by the camera module 1411, the image encoder1412 converts it into a specific image data format while burying intoeach image data the frame number being well synchronized among thecameras. The imaging timing-synchronized video data thus generated inthis way will be transferred via the network 104 to the videocollect/browse server 120.

In the surveillance system arranged to use the imaging-synchronizablesurveillance cameras with its remaining components being similar tothose of the first embodiment, image degradation and deterioration willno longer take place, such as doubly shifted or “ghosted” syntheticdisplay of the same land vehicle at a composite image portion of certainpart of the scene image 1101 indicative of the road states of multiplesurveillance cameras as buried in a map image such as shown in FIG. 11,which image portion is being repetitively acquired by a plurality ofcameras.

According to this embodiment, it becomes possible to synthesize foron-screen display several surveillance camera images in a map imagewhile achieving higher quality than the first embodiment. This in turnadvantageously makes it possible to obviate occurrence of thesurveillant's situation judging mistakes otherwise occurring due to theinaccuracy of merged images, in addition to similar effects to those ofthe first embodiment.

According to the embodiments explained previously, it becomes possibleto display, on a map in a centralized way, a plurality of surveillancecamera-captured video images different from one another in imagingdirection and imaging position plus imaging view angle while unitarilycompensating differences in on-screen visual appearance among theplurality of monitor camera images. Thus it is no longer required toindividually perform, in units of different monitor camera images, thereading and understanding of multiple monitor camera images insurveillance areas. This in turn makes it possible to readily recognizewithin the map the mutual relationship of imaging ranges of differentmonitor camera-captured videos, which leads to achievement of an effectthat the security officer's workload can be lightened.

The conceptual principles of the present invention may be utilizable tosurveillance or “watchdog” systems for traffic monitoring or formonitoring a wide range of area, such as shopping malls, public spaces,entire floors of buildings or equivalents thereto.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. An image generation apparatus connected to a plurality of imagingdevices for acquiring images from different directions, said apparatuscomprising: a unit receiving from said imaging devices image dataindicative of respective images as taken thereby; an extraction unitextracting a specified region in units of said image data; and asynthesis unit combining said extracted image data with map informationcontaining an imaging area of said imaging devices to thereby generatean image, wherein at least one of said plurality of imaging devices hasa synchronous reference counter, for sending and receiving, between saidplurality of imaging devices, synchronization information concerning asynchronization signal for use as a reference of imaging timing, foradjusting based on said synchronization information a readout value ofsaid synchronous reference counter, for generating a synchronizationsignal based on the readout value of said synchronous reference counter,and for controlling the at least one of said plurality of imagingdevices based on said synchronization signal.
 2. The image generationapparatus according to claim 1, further comprising: a unit retaining themap information containing the imaging area; and a conversion unitconverting a geometric shape of said image based on said mapinformation, wherein said extraction unit extracts a specified region ofsaid image data thus converted.
 3. The image generation apparatusaccording to claim 2, wherein said conversion unit performs conversionfor causing the specified region extracted at said extraction unit to beidentical in geometric relationship to said map information.
 4. Theimage generation apparatus according to claim 3, wherein said conversionunit performs conversion per imaging device based on a parameterindicative of correlation between a first position coordinate includedin said specified region of the image to be taken and a positioncoordinate of said map information corresponding to said first positioncoordinate.
 5. The image generation apparatus according to claim 2,wherein said extraction unit extracts from said image data converted bysaid conversion unit a region in which said image data and said mapinformation are identical in geometric relationship to each other. 6.The image generation apparatus according to claim 5, wherein theapparatus retains in advance mask information per imaging device forindicating a region in which the image data converted by said conversionunit is identical in geometric relationship to said map information, andwherein said extraction unit extracts, based said mask information persaid imaging device, a specified region from said image as taken by eachsaid imaging device.
 7. The image generation apparatus according toclaim 2, further comprising: a display unit displaying on a displayscreen the image synthesized by said synthesis unit.
 8. The imagegeneration apparatus according to claim 1, wherein: the at least one ofsaid plurality of imaging devices has a frame number generator foruniquely calculating a frame number from the readout value of saidsynchronous reference counter, the frame number generated by said framenumber generator being buried in units of acquired images, and saidimage generation apparatus synthesizes, based on the frame number buriedin an image to be received from each said imaging device, an image withits frame number being identical thereto and said map information.
 9. Animage display apparatus being connected to a plurality of imagingdevices for taking images from different directions and having a displayunit for displaying map information containing an imaging area of morethan one of said imaging devices, said apparatus comprising: aconversion unit converting an image acquired by each said imaging devicein such a way that a portion of the image is identical in geometricrelationship to a partial region of said map information, wherein: saiddisplay unit displays an image of a region out of the image converted bysaid conversion unit which is identical in geometric relationship tosaid map information in a display region for displaying said mapinformation in accordance with said geometric relationship, and at leastone of said plurality of imaging devices has a synchronous referencecounter, for sending and receiving, between said plurality of imagingdevices, synchronization information concerning a synchronization signalfor use as a reference of imaging timing, for adjusting based on saidsynchronization information a readout value of said synchronousreference counter, for generating a synchronization signal based on thereadout value of said synchronous reference counter, and for controllingthe at least one of said plurality of imaging devices based on saidsynchronization signal.
 10. The image display apparatus according toclaim 9, wherein: the at least one of said plurality of imaging deviceshas a frame number generator for uniquely calculating a frame numberfrom the readout value of said synchronous reference counter, the framenumber generated by said frame number generator being buried in units ofacquired images, and said image display apparatus synthesizes, based onthe frame number buried in an image to be received from each said imagedevice, an image with its frame number being identical thereto and saidmap information.
 11. An image synthesis method for combining togetherimages to be taken by a plurality of imaging devices, said methodcomprising the steps of: retaining map information containing an imagingarea; acquiring said images; converting each image based on a parametercorrelated per imaging device in such a manner that a partial region ofsaid image is identical in geometric shape to a specified region of saidmap information; extracting from the converted image an image of aregion which is identical in geometric shape to the specified region ofsaid map information; and combining together the extracted image andsaid map information, wherein at least one of said plurality of imagingdevices has a synchronous reference counter, for sending and receiving,between said plurality of imaging devices, synchronization informationconcerning a synchronization signal for use as a reference of imagingtiming, for adjusting based on said synchronization information areadout value of said synchronous reference counter, for generating asynchronization signal based on the readout value of said synchronousreference counter, and for controlling the at least one of saidplurality of imaging devices based on said synchronization signal. 12.The image synthesis method according to claim 11, wherein: the at leastone of said plurality of imaging devices has a frame number generatorfor uniquely calculating a frame number from the readout value of saidsynchronous reference counter, the frame number generated by said framenumber generator being buried in units of acquired images, and saidimage synthesis method has a step of synthesizing, based on the framenumber buried in an image to be received from each said imaging device,an image with its frame number being identical thereto and said mapinformation.
 13. An image generation system having a plurality of cameradevices and an image generation apparatus connected to respective onesof said camera devices via a network, wherein: each said camera devicehas an imaging unit for image acquisition and a unit for sending theimage thus acquired to said image generation apparatus, and said imagegeneration apparatus comprises: a storage unit retaining in advance mapinformation containing an imaging area; a unit receiving said image; aunit converting said image based on a parameter correlated per saidcamera device in such a manner that a partial region of said image isidentical in geometric shape to a specified region of said mapinformation; an extraction unit extracting from the converted image animage of a region identical in geometric shape to the specified regionof said map information; a unit synthesizing the extracted image andsaid map information to thereby generate an image; and a display unitdisplaying the synthesized image, and at least one of said plurality ofcamera devices has a synchronous reference counter, for sending andreceiving, between said plurality of camera devices, synchronizationinformation concerning a synchronization signal for use as a referenceof imaging timing, for adjusting based on said synchronizationinformation a readout value of said synchronous reference counter, forgenerating a synchronization signal based on the readout value of saidsynchronous reference counter, and for controlling the at least one ofsaid plurality of camera devices based on said synchronization signal.14. The image generation system according to claim 13, wherein: the atleast one of said plurality of camera devices has a frame numbergenerator for uniquely calculating a frame number from the readout valueof said synchronous reference counter, the frame number generated bysaid frame number generator being buried in units of acquired images,and said image generation apparatus synthesizes, based on the framenumber buried in an image to be received from each said camera device,an image with its frame number being identical thereto and said mapinformation.